diff --git a/test/test_feature_extractors.py b/test/test_feature_extractors.py
index f8de329..5286a31 100644
--- a/test/test_feature_extractors.py
+++ b/test/test_feature_extractors.py
@@ -310,7 +310,19 @@ class TestVideoActivityFeatureExtractor(unittest.TestCase):
         test_extractor.teardown()
         self.assertTrue(test_extractor.features)
 
-    # TODO: add sample video with activity to test _activitydetect()
+    def test_keep_num(self):
+        """Test keep_num keeps 0"""
+        num_features = 1
+        min_duration = 0
+
+        video_source = TestSourceMedia().one_colour_silent_audio()
+        test_extractor = extractors.VideoActivityFeatureExtractor(input_files=video_source,
+                                                                  num_features=num_features,
+                                                                  min_duration=min_duration)
+        test_extractor.setup()
+        test_extractor.run()
+        test_extractor.teardown()
+        self.assertEqual(len(test_extractor.features), num_features)
 
 class TestJSONFeatureExtractor(unittest.TestCase):
     """Test JSONFeatureExtractor"""